During the manufacturing of conductive structures in a semi-conductor device, like trenches, electrodes or vias, it usually is important to use a highly conductive layer which adheres well on the surface of a substrate like silicon. Furthermore, the choice of such material should as well satisfy some criteria as discussed below.
On one hand, the formation and further processing of the material should be compatible with standard semiconductor manufacturing processes. In addition, a conform layer is usually required, e.g., a layer should be formed uniform across a wafer and reproducible from wafer to wafer. Furthermore, the manufacturing process should be easy to implement and most importantly, cost attractive in comparison to standard procedures.
It is well known from the literature that conductive carbon containing materials, like polycrystalline carbon containing films known also as pyrocarbon, can be excellent candidates for semiconductor technology, e.g., for the fabrication of memory devices such as DRAM or Non-Volatile Memories (NVM).
The patent DE 103 45 393 A1 describes a method to deposit conductive carbon containing layers on a silicon substrate. The silicon surface is covered with silicon-oxide as a passivation layer. The method consists of introducing a wafer in a chamber at room temperature, to heat the chamber to 950° C. under H2 flow. Then the carbon containing layer is deposited by pyrolyse of CH4 at a pressure of 300 hPa to 800 hPa and at 950° C. Optionally after the deposition, the carbon containing layer may be annealed at a temperature of 1050° C. for 2 minutes.
The patent DE 10 2004 006 544 B3 describes a method of manufacturing MESFET transistors (Metal Semiconductor Field Effect Transistor) with a Schottky-gate consisted of a conductive carbon containing material.
G. Raghavan et al. describe in reference Jpn. J. Appl. Phys. Vol. 32(1993) pp. 380-383, the use of polycrystalline Carbon (in the reference it is named as well polycarbon) as a material for gate electrodes in MOS technology. The polycarbon films are deposited on oxidized silicon substrates at temperatures ranging from 700° C. to 1100° C. and at pressures ranging from 0.5 Torr to 2.0 Torr (˜66.7 Pa to 266.7 Pa). Oxide thicknesses are varied from 6.2 nm to 100 nm. Methane is used as the hydrocarbon precursor and boron trichloride is used to dope the polycarbon films. The technique of deposition consists of Plasma Assisted Chemical Vapour Deposition (PECVD) with an RF (Radio-Frequency) excitation at 13.56 MHz.
The patent DE 198 56 295 C2 describes a method of manufacturing Chemically Sensitive Field Effect Transistors (CHEMFET) wherein the gate electrode is a so called carbon-electrode. The carbon-electrode is formed of a carbon containing layer which is an organic (Novolack) material. The gate electrode is built on a silicon-oxide layer which is used as isolation layer on top of a silicon substrate.
Although conductive carbon films could be very attractive materials for semiconductor manufacturing, the application of these materials is up to now limited. In particular, there is a limitation for their application in trench capacitors (as for example MIM-like (Metal-Insulator-Metal) capacitor structures) or as Schottky diodes where at least one metal layer is formed by a conductive carbon containing layer on a silicon surface.
One factor limiting the application of carbon containing materials is the formation of a silicon-oxide layer on the surface of silicon substrate. The literature discloses well known wet-chemical treatments based on HF solution, to etch and remove the silicon-oxide native layer from the surface of silicon. However, during the deposition of conductive carbon containing films on a silicon surface, at temperatures between 600° C. and 900° C., the formation of a silicon-oxide interface is unavoidable. This silicon-oxide interface, although thin (less than 2 nm), results in appearance of an additional capacitive resistance which either reduces the performance or deteriorates the functionality of the devices as trench capacitors (like MIM) or Schottky diodes.
Bergmaier et al., in reference Diamond and Related Materials 8(1999) pp. 1142-1147, report the studies of the oxygen coverage at the diamond/Silicon interface, in a range of temperature between 700° C. and 850° C.
A second factor limiting the use of carbon containing materials in devices, as trench capacitors (like MIM) or Schottky diodes, is the formation of side products as particles, in particular polymeric carbon products, from carbon containing gas. Although conform layers could be easily deposited from carbon containing gases, a so-called substantially soot (particle)-free process is a due for semiconductor applications in aim to avoid a yield loss by parasitic particles.
Oberlin reports in reference Carbon 40(2002) pp. 7-24, the micro-structural studies of pyrocarbon films related to the decomposition of hydrocarbon gases and chemical reactions in the gas phase. It was reported in this reference that by using C2H2 as gas, droplets (homogeneous nucleation in the gas) form parasitic soot which would subsequently deposit on the substrate.